1. Field of the Invention
The present invention relates to a voice signal clipping circuit that clips excessive amplitude of an input voice signal, and a telephone set having the voice signal clipping circuit.
2. Description of the Related Art
Conventionally, telephone exchanges such as a private branch exchange (PBX) and a key telephone system are used in many cases in office buildings and business offices. These kinds of telephone exchanges include telephone sets as extension terminals for example, and perform exchanges between the extension terminals and external communication networks like public networks and between the extension terminals to establish communications.
Some telephone sets have volume adjusting circuits to obtain proper reception volume. However, when the volume is increased, a noise component mixed in the voice signal is also amplified, which may make it difficult to catch voice.
To overcome this difficulty, a unit that clips excessive amplitude of the voice signal amplified by the volume adjusting circuit and reduces the amplitude set in the volume adjusting circuit in response to the clipping operation is proposed (refer to Jpn. Pat. Appln. KOKAI Publication No. 5-183622).
Some telephone exchanges are connected with analog telephone sets, digital telephone sets, and IP telephone sets that are not provided with the volume adjusting circuit, in addition to the telephone sets having the volume adjusting circuit. When voice signals of a level larger than a rated input is input to large-scale integrated circuits (LSI) of these telephone sets that process the voice signal, the other communication parties receive a distorted voice. Therefore, it is strongly desired to take measures to prevent the distortion of a voice in the telephone set that do not have the volume adjusting circuit even if a voice signal larger than the rated input is input to the LSI.